Houston ? The Justice Department is investigating contacts between the Federal Reserve Board and Enron Corp. and has told the central bank not to destroy any documents related to the bankrupt energy giant.

It is unclear what paper trails investigators are pursuing. But Enron enjoyed special access to the Federal Reserve along with other institutions, including the White House, Congress and state public utility commissions.

Both Kenneth Lay and Jeff Skilling, former Enron chief executives, met with Fed Chairman Alan Greenspan and other staff members over the past two years, and Skilling served as a director for a Federal Reserve branch bank in Houston.

Top officials with the Justice Department and the Fed declined to comment on the inquiry, as did Enron officials. But a senior economist with the Houston branch acknowledged that authorities have alerted the agency not to shred documents, including correspondence between the Fed and Enron.

“The Justice Department request involved all Enron-related materials,” said the economist, Bill Gilmer, who is also a vice president for the Houston branch.

The Federal Reserve influences the country’s money and credit supplies by overseeing banks and advising the U.S. government. It is unclear what help Lay might have sought from the Fed as his company failed, but he asked Bush administration officials at the time to intervene with credit-rating agencies, whose decision to downgrade Enron’s credit forced the company to pay its debts immediately.

Whether the Federal Reserve was a key strand in Enron’s wide-ranging net of influence, and whether the banking system helped the company are among the questions federal investigators are exploring, said Fed sources, who spoke on condition of anonymity.

Experts familiar with the inner workings of the Fed said they doubt that Enron wielded substantial influence over the federal banking system.

“I just don’t believe it (Enron’s access to the Fed) factored heavily in the big picture of setting national economic policy,” said James Pearce, a Fed economist from 1978 to 1980. “And I’m not sure where the political influence would have gotten them much.”

Enron executives had Greenspan’s ear in both public and private settings.

Lay phoned the powerful Fed chairman, along with other government officials, to discuss his company’s troubles. Details of the conversation have not been divulged, but Greenspan’s representatives said he took no action on behalf of Enron.

In response to a Knight Ridder request for all Enron-related documentation, the Fed released papers involving Skilling’s service as a member of the Houston branch’s board from February 2000 to January 2002. He resigned shortly before he began testifying to congressional committees examining Enron’s collapse.

In December 2000, Skilling gave Greenspan and other board members for the Federal Reserve Bank of Dallas an in-depth presentation on new Enron ventures and their economic impact, according to Skilling’s notes. The Dallas bank, one of 12 regional banks operated by the Fed, oversees the Houston branch.

Such presentations are rare for board members, former and current Fed officials said.